Various compasses which measure the horizontal component of the earth's magnetic field and provide an indication of magnetic heading are known in the prior art. One type of well known compass includes fluxgate attitude sensors in the form of magnetometers, which in addition to providing an indication of heading also provide an indication of the pitch and roll angles of the sensors relative to a horizontal plane. Such sensors are commonly used in towed array configurations for underwater seismic exploration. One such fluxgate compass is described in U.S. Pat. No. 5,170,566, issued to J. Thomas Fowler and George E. Selecman on Dec. 15, 1992, which is assigned to the assignee of the present invention, and which is hereby incorporated by reference.
Fluxgate compasses typically include two orthogonally disposed fluxgate magnetometers for measuring the horizontal component of the earth's magnetic field. Each magnetometer defines a sensing axis and measures the strength of the component of the earth's magnetic field that is parallel to its sensing axis. Each magnetometer is mounted on a gimbaled platform that uses counterweights to maintain the magnetometer, and its sensing axis, in a horizontal orientation. The sensing axes are typically referred to as the X and Y axes. One magnetometer therefore measures the X component H.sub.x of the earth's magnetic field, and the other magnetometer measures the Y component H.sub.y. An indication of heading, (i.e., the direction of heading with respect to magnetic north), is provided by the function shown in Equation (1). ##EQU1##
Fluxgate compasses also often include an additional sensor for measuring the vertical component H.sub.z of the earth's magnetic field. This vertical sensor is sometimes implemented as two orthogonally disposed magnetometers that are fixed, or "strapped down", to the frame of the compass, and is sometimes implemented as a single magnetometer mounted on a gimbaled platform such that the magnetometer remains in a vertical orientation. Measuring the vertical component is useful since the accuracy of the heading indication provided by Equation (1) varies with latitude, and by using the measured H.sub.z component it is possible to use known methods to provide correction terms for Equation (1) so that heading may be accurately measured at any latitude.
As stated above, fluxgate attitude sensors contain additional devices for measuring the pitch and roll angles of the sensor relative to a horizontal plane. These additional devices may be implemented as excitation coils, sometimes referred to as Helmholtz coils, wound around the outside of the platform supporting the sensors so that the platform moves relative to the coils. Pitch and roll measurements are made by monitoring the X and Y magnetometers while the excitation coils are sequentially energized.
One problem with such prior art devices is that the gimbaled platforms use slip rings, conductive bearings, or other such connectors which rely upon physical contact to establish an electrical connection between the magnetometer and an external sensing circuit. Such "contact-type" connections are disadvantageous because they create friction that limits the leveling accuracy of the gimbals. Further, they do not provide a high quality electrical connection and may form an open circuit when the sensor is subjected to sudden movements or impacts and thus cause an interruption, or a "glitch", in the operation of the device. Also, such connectors are prone to wear and tend to limit the useful lifetime of the device.
There is therefore a need for a fluxgate compass that does not use "contact-type" connectors to provide electrical connection to the gimbaled magnetometers.